I've found on some cars (i.e. Jeeps), disconnecting the antenna is insufficient. It just lowers the range of the cellular modem. If you get close enough to a ce

I've found on some cars (i.e. Jeeps), disconnecting the antenna is insufficient. It just lowers the range of the cellular modem. If you get close enough to a cell tower it'll still find a connection to the mothership. In my case I had to open the radio and physically remove the cellular modem. Which was thankfully on its own removable module.